1. Field of the Invention
The present invention relates to a thin film type solar cell, and more particularly, to a thin film type solar cell with a plurality of unit cells connected in series.
2. Discussion of the Related Art
A solar cell with a property of semiconductor converts a light energy into an electric energy.
A structure and principle of the solar cell according to the related art will be briefly explained as follows. The solar cell is formed in a PN-junction structure where a positive (P)-type semiconductor makes a junction with a negative (N)-type semiconductor. When a solar ray is incident on the solar cell with the PN-junction structure, holes (+) and electrons (−) are generated in the semiconductor owing to the energy of the solar ray. By an electric field generated in a PN-junction area, the holes (+) are drifted toward the P-type semiconductor and the electrons (−) are drifted toward the N-type semiconductor, whereby an electric power is produced with an occurrence of electric potential.
The solar cell can be largely classified into a wafer type solar cell and a thin film type solar cell.
The wafer type solar cell uses a wafer made of a semiconductor material such as silicon. In the meantime, the thin film type solar cell is manufactured by forming a semiconductor in type of a thin film on a glass substrate.
With respect to efficiency, the wafer type solar cell is better than the thin film type solar cell. However, in the case of the wafer type solar cell, it is difficult to realize a small thickness due to difficulty in performance of the manufacturing process. In addition, the wafer type solar cell uses a high-priced semiconductor substrate, whereby its manufacturing cost is increased.
Even though the thin film type solar cell is inferior in efficiency to the wafer type solar cell, the thin film type solar cell has advantages such as realization of thin profile and use of low-priced material. Accordingly, the thin film type solar cell is suitable for a mass production.
The thin film type solar cell is manufactured by sequential steps of forming a front electrode on a glass substrate, forming a semiconductor layer on the front electrode, and forming a rear electrode on the semiconductor layer. In this case, since the front electrode corresponds to a light-incidence face, the front electrode is made of a transparent conductive material, for example, ZnO. With the increase in size of substrate, a power loss increases due to a resistance of the transparent conductive layer.
Thus, a method for minimizing the power loss has been proposed, in which the thin film type solar cell is divided into a plurality of unit cells connected in series. This method enables the minimization of power loss caused by the resistance of the transparent conductive material.
Hereinafter, a related art method for manufacturing a thin film type solar cell with a plurality of unit cells connected in series will be described with reference to FIG. 1(A to F).
FIG. 1(A to F) is a series of cross section views illustrating a related art method for manufacturing a thin film type solar cell with a plurality of unit cells connected in series.
First, as shown in FIG. 1(A), a front electrode layer 20a is formed on a substrate 10, wherein the front electrode layer 20a is formed of a transparent conductive material such as ZnO.
Next, as shown in FIG. 1(B), a plurality of first separating channels 25 are formed by removing predetermined portions of the front electrode layer 20a, so that a plurality of front electrodes 20 are formed at fixed intervals by each first separating channel 25 interposed in-between.
Then, as shown in FIG. 1(C), a semiconductor layer 30a is formed on an entire surface of the substrate 10 including the front electrodes 20.
As shown in FIG. 1(D), a plurality of contact portions 35 are formed by removing predetermined portions of the semiconductor layer 30a. 
As shown in FIG. 1(E), a rear electrode layer 50a is formed on the entire surface of the substrate 10.
As shown in FIG. 1(F), a plurality of second separating channels 55 are formed by removing predetermined portions of the rear electrode layer 50a and the semiconductor layer 30a. Thus, a plurality of rear electrodes 50 are formed at fixed intervals by each second separating channel 55 interposed in-between, wherein each rear electrode 50 is electrically connected with the front electrode 20 by the contact portion 35. According as each rear electrode 50 is electrically connected with the front electrode 20 by the contact portion 35, the thin film type solar cell is formed in such a structure that a plurality of unit cells are electrically connected in series.
However, the related art method for manufacturing the thin film type solar cell has the following disadvantages.
First, the related art method for manufacturing the thin film type solar cell necessarily requires the total three patterning steps, that is, the patterning step for the first separating channel 25, the patterning step for the contact portion 35, and the patterning step for the second separating channel 55. These patterning steps are respectively performed by a laser-scribing process. In this case, the remnant may remain in the substrate during carrying out the laser-scribing process. Furthermore, if the substrate is contaminated by the remnant, a short may occur between the electrodes due to the remnant, whereby a cleaning process for removing the remnant from the substrate is generally carried out after performing the laser-scribing process. As a result, the cleaning process has to be carried out three times in the case of the related art method for manufacturing the thin film type solar cell which necessarily requires the total three patterning steps. That is, the related art manufacturing method becomes complicated and causes the low yield.
Second, the related art method for manufacturing the thin film type solar cell is comprised of vacuum-conditioned and atmosphere-conditioned processes which are performed alternately, so that a manufacturing apparatus is complicated in its structure, and a manufacturing time is increased, thereby lowering the yield.
To be brief, the related art method for manufacturing the thin film type solar cell is comprised of the process of forming the front electrode layer 20a (the process of FIG. 1(A)), the process of forming the first separating channel 25 (the process of FIG. 1(B)), the process of forming the semiconductor layer 30a (the process of FIG. 1(C)), the process of forming the contact portion 35 (the process of FIG. 1(D)), the process of forming the rear electrode layer 50a (the process of FIG. 1(E)), and the process of forming the second separating channel 55 (the process of FIG. 1(F)).
At this time, the process of forming the front electrode layer 20a (the process of FIG. 1(A)), the process of forming the semiconductor layer 30a (the process of FIG. 1(C)), and the process of forming the rear electrode layer 50a (the process of FIG. 1(E)) are generally performed by using a vacuum-deposition apparatus. Meanwhile, the process of forming the first separating channel 25 (the process of FIG. 1(B)), the process of forming the contact portion 35 (the process of FIG. 1(D)), and the process of forming the second separating channel 55 (the process of FIG. 1(F)) are generally performed by using a laser-scribing apparatus under the atmospheric pressure. In order to complete the related art thin film type solar cell, the substrate 10 has to be alternately loaded into the vacuum-deposition apparatus and the laser-scribing apparatus.
There is a need to prevent the outside air from flowing in the vacuum-deposition apparatus when loading the substrate 10 under the atmospheric pressure into the vacuum-deposition apparatus. Instead of directly loading the substrate 10 into the vacuum-deposition apparatus, the substrate 10 is generally loaded by passing through a road rock chamber so as to prevent the outside air from flowing in the vacuum-deposition apparatus. If the substrate 10 is alternately loaded into the vacuum-deposition apparatus and the laser-scribing apparatus, the apparatus structure becomes complicated due to the road rock chamber. Also, according as the substrate 10 passes through the road rock chamber, a time period for the manufacturing process becomes increased.